Gas turbine engines are typically employed to power aircraft. Typically a gas turbine engine will comprise an axial fan driven by an engine core. The engine core is generally made up of one or more turbines which drive respective compressors via coaxial shafts. The fan is usually driven off an additional lower pressure turbine in the engine core.
The fan comprises an array of radially extending fan blades mounted on a rotor. The fan blades and/or a casing that surrounds the fan may be manufactured from composite laminate materials. Generally composite fan blades include a composite body and may be provided with a metallic leading edge and/or a metallic trailing edge.
Composite components are often laminate structures that include a plurality of plies. Each ply generally includes reinforcing fibres (e.g. high strength and/or high stiffness fibres) embedded in a matrix, e.g. a plastic matrix material. The matrix material of adjacent stacked plies is bonded together to build the composite component. A primary failure mechanism of concern for composite materials is delamination. Delamination for example of a fan blade may occur in the event of an impact by a foreign object such as a bird strike
Delamination may occur in mode I failure or mode II failure. As is understood in the art, mode I is inter-laminar cracking where the plies of the laminate peel apart, and mode II is inter-laminar cracking where the plies slide over one another.
Various tests have been devised to determine how a composite laminate component will behave in mode II fatigue failure. To test fatigue failure in a composite component it is necessary to apply reverse loading to the composite component. This has been done using a three point bend test arrangement or by using a cantilever arrangement.
An example of a cantilever arrangement includes incorporating a film in the composite component as a crack initiator and then clamping the component at one end. Load is applied to the opposite end using an arrangement of pins and a plurality of bearings. However, this method of testing includes a complicated loading device and as such the loading is more difficult to control and there is an increased likelihood of failure. Furthermore, the testing equipment can often experience unwanted loads that can affect the fatigue life of the component.
An alternative cantilever arrangement test includes incorporating a film in the composite component as a crack initiator and then clamping the component at one end. A ram is attached to the clamped end to move the end up and down. The opposite end of the component is clamped between two hardened steel rollers that are connected to a load cell. However, in this test method the steel rollers can induce stress concentrations in the component. Furthermore, the component may experience unwanted oscillations and unwanted dynamic affects during a loading cycle that can affect fatigue life of the component.
There is a desire in the industry for an improved rig and method of testing composite components.